Symposium CC
Materials Solutions for Highly Demanding Tribological Applications

Session CC-1 - Fundamentals of Friction, Wear, Adhesion and Lubrication

CC-1:IL02  Dissipation in Nanoscale Systems: from Nanotubes to Water
E. RIEDO, School of Physics, Georgia Institute of Technology, Atlanta, GA, USA

Experiments on dissipations processes in nanoscale systems will presented in this lecture. In particular atomic force microscopy studies of dissipation-elasticity entanglement effects in nanotubes will be discussed. Furthermore, we will present recent results on the viscosity of nanoconfined water, and the relation between viscous dissipation in confined water and the chemistry of the confining surfaces. In general we will show how at the nanoscale dissipation phenomena are strongly related to the geometry, elasticity and chemistry of the interacting systems.
Deborah Ortiz-Young, Hsiang Chih Chiu, Suenne Kim, Kislon Voitchovsky and Elisa Riedo "The interplay between apparent viscosity and wettability in nanoconfined water", Nature Communications, DOI: 10.1038/ncomms3482 (2013).
Marcel Lucas, Xiaohua Zhang, Ismael Palaci, Christian Klinke, Erio Tosatti, and Elisa Riedo "Hindered rolling and friction anisotropy in supported carbon nanotubes" Nature Materials 8, 876 (2009).


CC-1:IL03  Structural and Mechanical Modifications of Hard Carbon Coatings Lubricated with Glycerol Studied by FIB-EFTEM
M.I. DE BARROS BOUCHET, Ecole Centrale de Lyon, Laboratory of Tribology and System Dynamics (LTDS), Ecully, France

The physical, chemical and mechanical properties of nanocrystalline diamond (NCD) and diamond-like carbon coatings (DLC) were investigated by Energy-Filtering TEM (EFTEM) analysis coupled with a new technique of samples preparation, Focused Ion Beam (FIB). Carbon coatings presenting different tribological behaviors under boundary lubrication regime with glycerol and Glycerol Mono-Oleate (GMO), were studied. EELS appears like a very powerful technique to characterize such carbon coatings. A special attention was paid to the maximum energy of the plasmon peak which was used to evaluate some physical and mechanical properties of coatings (density, hardness,.). For ta-C coating, EFTEM results show a strong re-arrangement of the DLC bulk structure under the friction process. Typically, the transformation of sp3 carbon into sp2 carbon was clearly observed. This corresponds to a self-adaptation of the coating allowing him to support shearing without any delamination in spite of the important intrinsic compressive residual stresses inside the coating. Moreover, the formation of a sp2-carbon rich layer is evidenced at the top surface. This sp2-carbon rich layer certainly helps the lubrication mechanism by glycerol in forming OH-terminations when the dangling bonds occur in the contact.


CC-1:IL05  Fundamentals of Elastohydrodynamic Lubrication
M. KANETA¹, P. YANG², I. KRUPKA¹, M. HARTL¹, ¹Brno University of Technology, Brno, Czech Republic; ²Qingdao Technological University, Qingdao, P.R.China

The lubrication of machine elements having a concentrated contact between non-conforming surfaces, such as rolling element bearings, gears and cam and tappet, is named as elastohydrodynamic lubrication (EHL), because the contacting surfaces are significantly deformed due to high contact pressures. EHL is arguably one of the greatest achievements in tribology studies of the 20th century, and has contributed very much to the improvement of performance, reliability and durability of machinery. This is because the direct observations of phenomena occurring between contacting surfaces have been made possible by means of the optical interferometry technique and the results are well correlated to the numerical analysis. Furthermore, the EHL theory can predict the film thickness profile fairly accurately by knowing the working conditions at the entrance to the contact; the film thickness is not influenced by the sliding velocity if the entrainment velocity is maintained constant. However, recently it has been found that the film thickness and pressure are influenced very much by the slide-roll ratio, geometry of the contact and the thermal conductivity of contact materials. These fundamentals will be presented and discussed in steel-steel and Si3N4-steel contacts.


Session CC-2 - Coatings, Surface Engineering and Nanostructuring

CC-2:IL01  Silicon Diamond-like Coatings
L.V. SANTOS^{1, 2},  F.L.C. LUCAS¹, R.S. PESSOA^{1, 2}, H.S. MACIEL^{1, 2}, M. MASSI^{2, 3}, F. GALEMBECK^{4, 5}, ¹University of Paraiba Valley IP&D/UNIVAP, Sao Jose dos Campos - SP, Brazil; ²Technologic Institute of Aeronautics, ITA/CTA, Sao Jose dos Campos - SP, Brazil; ³Institute of Science and Technology, ICT/UNIFESP, Sao Jose dos Campos - SP, Brazil; ⁴Institute of Chemistry, University of Campinas - UNICAMP, Campinas SP, Brazil; ⁵National Nanotechnology Laboratory at the National Center for Energy and Materials Research, Campinas SP, Brazil

During the last few decades great interest has been attracted by diamond-like carbon (DLC) as protective coating. As a chameleon it name is changed according with sp2 and sp3 Raman spectra bands position: amorphous carbon a-C; tetrahedral amorphous carbon ta-C; hydrogenated amorphous carbon a-C:H and each coating with a specific chemical, mechanical and tribological properties. Metallic and non-metallic particles also have been used to improved life time and upgrade the diamond-like coating as a bactericide, fungicide or both. There is no doubt that DLC is a modern coating. If so, does it possible upgrade something that is so good?
Neither doped diamond-like nor carbon alloy coatings with more than one part per million and lower than an intermetallic compound with no distinct boundary between the phases, is the new Silicon diamond-like (DLSi), Silver Diamond-like (DLAg); and Gold Diamond-like(DLAu) coatings. This paper presents the deposition coating methodology u sing direct liquid injection by Plasma Enhanced Chemical Vapor Deposition (DLI-PECVD) and also bulk structure, tribological and corrosion results from this new diamond-like as a forever coating for many applications.


CC-2:IL02  Tribological Properties of Carbon Layers Derived from Different Polytypes of Silicon Carbide
DAE-SOON LIM, MIN-GUN JEONG, EUNGSUK LEE, Department of Materials Science and Engineering, Korea University, Seoul, Korea

The tribological performances of carbide derived carbon (CDC) layer are significantly improved due to the formation of low frictional layer. In this study, effect of the polytypes of silicon carbide on the formation of nano-crystalline structures and tribological properties was investigated. CDC layers were synthesized from α-SiC and β-SiC substrate by selective etching process in chlorine and hydrogen gas mixture at high temperature. The content of carbon phase and crystallinity were analysed by Raman spectroscopy. Nano-crystalline phases of synthesized CDC were characterized by transmission electron microscopy. Tribological properties were tested with pin-on-disk type tribometer. The carbon structures of CDCs are influenced with SiC polytypes, reaction temperature and gas fractions. Graphitic carbon was frequently observed in β-SiC-derived carbons. Diamond nano-crystals were found in α-SiC-derived carbons and sp3- bond was increased with adding more hydrogen gas. The friction coefficients of β-SiC-derived carbons were decreased due to the content of graphitic carbons. The variation of nano-crystalline phase correlated with the tribological and mechanical properties. A possible mechanism responsible for the observed results is discussed.


CC-2:IL03  Advances in Ti-Al-N and other Nanocomposite Coatings for Severe Applications
P.H. MAYRHOFER, Institute of Materials Science and Technology, Vienna University of Technology, Vienna, Austria

This work summarizes recent developments on applying thin film structure and architecture concepts to hard coatings for optimized performance in various application fields.
The hardness of materials rapidly decreases at elevated temperatures as generally the density of structural defects, such as point defects, dislocations, and grain boundaries, decreases. Additional strengthening can be provided by age-hardening mechanisms, which originate from decomposition-processes of supersaturated phases to form new obstacles retarding plastic deformation. Furthermore important is the resistance against oxidation and corrosive attack.
By using ab initio calculations and sophisticated experimental methods we will have a detailed insight into various mechanisms responsible for excellent mechanical strength, thermal stability and oxidation resistance properties of Ti–Al–N based hard coatings. For these materials we will also compare the effect of various architecture and alloying concepts with e.g., Y, Zr, Hf, Nb, and Ta.
The various thin film structure and architecture concepts allow the utilization of multifunctional properties facilitating the development of next generation's hard coatings.


CC-2:IL04  Cathodic Arc Plasmas in Surface Engineering
M. URGEN, S. ÖNCEL, T. TURUTOGLU, K. KAZMANLI, Istanbul Technical University, Department of Metallurgical and Materials Engineering, Maslak-Istanbul, Turkey

Cathodic arc plasma generated by the initiation and propagation of an arc on the metallic targets in a vacuum environment results in almost totally ionized metal vapors. The character of the plasma allows us to treat substrates in different manners. Application of a negative potential (bias potential) to the substrate results in bombarding of the substrate surface with the metal ions, energy of which depends on the magnitude of potential. We benefit from ion bombardment effects for heating and sputter cleaning of the substrates (high bias voltages) prior to initiation of the deposition process and also for densifying the coating structure (low bias voltages). Another possibility is to heat the substrates by electrons with supplying positive voltages to the substrates. Both of these approaches are used for coating production with cathodic arc PVD.
In this presentation, the possibility of the production of well adherent and dense metallic coatings on ceramic and diffusion layers on metallic substrates by the application of positive and negative bias voltages to the substrates will be introduced. The motivation behind this attempt is the very fast and controlled heating possibilities of the substrates both by positive and negative bias applications. Examples of applications for Ti and TiAl deposition on ceramics and aluminizing of Ni and Ti alloys will be given. Results of the studies showed that it is possible to produce very well adherent and dense metallic layers on ceramic substrates and thick aluminide layers on different metallic substrates in short duration of process times.


CC-2:IL05  Tribological Performance of Textured Coatings
TIANMIN SHAO, XIMEI WANG, XIAO HUANG, HONGFEI SHANG, SHIYU HU, State Key Laboratory of Tribology, Tsinghua University, Beijing, China

It is well known that tribological performance of materials could be improved by producing coatings on their surfaces. In recent years, research work revealed that friction, wear and lubrication could also be effectively controlled by fabricating desirable patterns on material surfaces. Such a technique is named surface texturing. In this work, a technique combining surface coating and surface texturing is introduced. Textured thin solid nitrides coatings are produced by masked deposition with both multi arc plating and ion beam assisted deposition systems. Mechanical properties of the coatings are studied by nano-indentation test and scratch test. Residual stress of the coatings is analyzed with a substrate curvature method using Stoney's Equation to calculate the value of the residual stress. Tribological performance is studied with a friction and wear tester. Comparison of both the coating properties and the tribological performance is made between the textured coatings and the full coatings. Comparing to the full coatings, the textured coatings demonstrated an evidently improved tribological performance. Mechanism of the improvement in tribological performance is discussed.


CC-2:L06  Design of Catalytically Active Nanocomposite Ceramic Coatings for DLC Boundary Film Formation on Lubricated Sliding Surfaces
A. ERDEMIR, O. ERYILMAZ, Argonne National Laboratory, Energy Systems Division, Argonne, IL, USA

In this study, we designed a series of catalytically active nitride-based ceramic coatings that can extract diamondlike carbon (DLC)-based boundary films from synthetic, mineral, and vegetable-base lubricating oils at sliding contact interfaces. These nanocomposite coatings were produced by a magnetron sputter ion plating technique and by introducing some known catalysts (such as Pd, Ag, Cu, Ni, etc.) into the harder nitride phases of Mo, W, V, and Re, etc. (which are also catalytically active). When such films are tested under severe boundary lubricated sliding conditions, a carbon-rich boundary film having essentially the same kinds of structural chemistry as traditional DLC films is produced on sliding surfaces. UV Raman and a variety of other surface and structure analytical techniques confirmed the DLC-like structural chemistry of such films which were found to provide very low friction and wear coefficients even under extreme sliding conditions. They were also very resistant to scuffing able to provide long wear life under starved lubrication conditions. In this presentation, we will provide further insight into the structural, chemical, and tribological properties of these designer coatings and explain the underlying mechanisms for their impressive tribological properties under severe operating conditions.


CC-2:L07  The Influence of Alumina and Zirconia Coats on the Tribological Properties of Alumina NanoFibers
M. AGHAYAN¹, M. GASIK², L. KOLLO¹, I. HUSSAINOVA¹, M. RODRÍGUEZ³, ¹Tallinn University of Technology, Department of Materials Engineering, Tallinn, Estonia; ²Aalto University Foundation, School of Chemistry, Material Science and Engineering, Aalto, Finland; ³Instituto de Cerámica y Vídrio (CSIC), Campus Cantoblanco, Madrid, Spain

Alumina Nanofibers (ANF) with 7 nm in diameter were covered with ZrO2 and Al2O3 by chemical liquid deposition (CLD) method in order to study the influence of ZrO2 and Al2O3 on the tribological properties of ANF. The quantity of both zirconia and alumina was 10 vol.% of ANF. The zirconia-coated, alumina-coated and uncoated ANFs were capsulated by steel in vacuum at 1200 oC. The obtained capsules were pressed by HIP. The densities of the samples were measured before and after sintering. The porosity was examined by terahertz spectroscopy. The composition and structure of synthesized and sintered materials were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM). The tribological properties of samples were studied.


Session CC-3 - Friction and Wear at Micro/Nanoscale

CC-3:IL01  Mapping Tribological Mechanisms in Corrosive Environments: Application to Energy Conversion Processes
M.M. STACK, Department of Mechanical and Aerospace Engineering, University of Strathclyde, Glasgow, UK

Tribological interactions with corrosion may occur in a wide range of environments, from oil and gas conversion, advanced coal conversion processes, bio-medical implants, to wave, wind and tidal energy conversion.  In such cases, the extent of mechanical and chemical interactions can differ greatly.  As a result, defining a rationale for describing the degradation mechanisms is of importance, in order to provide a methodology for control of such issues in practice.
In energy conversion, there are wide variations in process temperatures, surface chemistries, and tribological variables.  This means that there are many possible solutions to materials selection in such conditions.  Tailoring a material or a coating to a tribo-corrosion application provides a means of selection “smart” materials for various tribo-corrosion systems.
This talk will consider a range of tribo-corrosion issues in energy conversion.  It will explore how such issues can be grouped in terms of the tribo-corrosion regime and degradation rate.  Strategies towards providing tribo-corrosion regime “envelopes” for energy conversion,  based on these trends, will also be addressed in this presentation.


CC-3:IL02  Nano/Micro-Tribology of MEMS
M.T. DUGGER, Sandia National Laboratories, Albuquerque, NM, USA

Micro- and NanoElectroMechanical Systems (MEMS and NEMS) have advanced dramatically in the last two decades with the maturation of several microfabrication technologies. Lubrication of these small machine elements still presents unique challenges. Selectively placing solid lubricants where they are needed using procedures compatible with fabrication processes, or using liquid lubricants that do not interfere with device operation, becomes increasingly complex as the size of machine parts decreases. The tribological challenges associated with MEMS/NEMS devices and solutions to friction and wear issues will be reviewed. Particular emphasis will be given to Vapor Phase Lubrication (VPL), which is an effective approach for lubricating small precision mechanisms. VPL requires no coating deposition and uses no bulk fluid that can damp device motion, but rather involves the passivation of surfaces by equilibrium adsorption of molecules from the vapor phase in a controlled atmosphere. This facile but limited adsorption is the critical characteristic for successful lubrication of MEMS devices, in which capillary adhesion can exceed the force available from actuators. Vapor phase lubrication has also been shown to be effective on alloy surfaces.


CC-3:IL03  Micro-wear Characteristics of Thin Coatings for Tribological Applications
DAE-EUN KIM, School of Mechanical Engineering, Yonsei University, Seoul, Korea

Coatings are extensively utilized in tribological applications to achieve the desired level of friction and wear properties. Considering the abundance of candidate materials and the diverse methods that can be used to deposit the coating on the target substrate, optimizing the tribological properties of the coating for a given application is a challenging task. In this regard, the fundamental mechanisms underlying the friction and wear of thin coatings need to be better understood. In this presentation, the micro-wear characteristics of homogeneous thin coatings as well as nano-composite coatings are discussed. The wear track generation characteristics of pure metallic thin coatings together with local frictional behavior along the wear track are presented. Also, the tribological properties of nano-composite coatings consisting of carbon nanotube fibers are explored. Better understanding of the wear characteristics of these coatings are expected to aid in development of superior functional coatings for tribological applications.


CC-3:L04  The Effect of Submicron Si3N4 Particles on Wear Resistance of Al-based Alloys
M. SOPICKA-LIZER¹, J. MYALSKI¹, D. MICHALIK¹, N. VALLE²,  G. LIPPMANN², A. BOTOR-PROBIERZ², T. PAWLIK¹, ¹Silesian University of Technology, Gliwice, Poland; ² Centre de Recherche Public (CRP-GL), Luxembourg

Reinforcement of aluminium-based alloys by ceramic particles has been known for decades but tribological properties of these composites are only moderately improved because of particles pulling out and formation of hard debris between working surfaces. The aim of this work was to reduce ceramic particles to submicron level and to introduce them homogeneously in the metal matrix. Mechanochemical processing for manufacturing Al-Si3N4 composite particles was employed followed by high-pressure isostatic pressing and densification above alloy melting temperature. Tribological properties were tested under various parameters and microstructural observation of as-received and worn-out specimen were performed. The results show the significant effect of particle size and type of particle-matrix bonding on the wear resistance.

 
Session CC-4 - Biotribology

CC-4:IL01  An Overview of Coatings for Articulating Medical Implants
R. HAUERT, K. THORWARTH, Empa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland; G. Thorwarth, Synthes GmbH, Dübendorf, Switzerland

Some hard coatings such as diamond-like carbon (DLC) show extremely low wear in technical applications. A desired medical implementation is to build wear particle free articulating joint replacements. In vivo studies using DLC coatings on articulating joints resulted in failures some years after implantation, due to unpredicted coating delamination. It will be shown that in some cases a delayed in vivo delamination was caused by crevice corrosion (CC) of the adhesion-promoting interlayer. Furthermore, at the coating/substrate interface a few atomic layers of reaction products are formed controlling coating adhesion. Any small contamination from residual gas or any cross contamination will result in a different reactively formed interface material with varied properties. Delamination can occur by a slowly advancing crack in this thin interface material governed by the laws of stress corrosion cracking (SCC). It will be shown that if a stable coating adhesion is obtained, DLC coated articulating implants show basically no wear of the coating up to 101 million cycles of articulations on a simulator corresponding to about 101 years of in vivo articulation. A main issue for in vivo applications of coated implants is to predict the long-term adhesion stability of the coating.


CC-4:IL02  Tribological Behavior of Hip Replacements
E. CIULLI, F. DI PUCCIO, L. MATTEI, Department of Civil and Industrial Engineering, University of Pisa, Pisa, IT; S. Affatato, S. Battaglia, Istituto Ortopedici Rizzoli, Bologna, Italy

Since 1960, when the first hip prosthesis was introduced, up to now, several implant typologies have been proposed trying to meet the increasing clinical demands of more and more active and young patients. A substantial evolution of implant design has been occurring, both in terms of materials and geometry, basically driven by their tribological performances. Indeed, the main concern of hip implants consists in the release of wear debris which can lead to implant loosening and failure. Thus, many studies on wear and lubrication of hip prostheses have been published in the last 15 years mainly focused on experimental researches but also on numerical/modeling approaches. Recently, for Metal on Metal implants, a new lubrication mechanism has been identified, caused by the aggregation of proteins at the inlet, and the contribution of corrosion on surface damage has been reckoned. Modeling the tribological behavior of these components could help to enhance the comprehension of their actual working conditions, to simulate long term and complex loading history and to improve the implant design itself. This work reviews the history of hip implants from a tribological point of view, analysing both numerical models and experimental wear data, with a special focus on ceramic solutions.


Session CC-5 - New Theory and Computer Simulations

CC-5:IL01  Atomic-scale Friction, Peeling and Shear in Carbon and Silicon Nanostructures
N. SASAKI, K. MIURA, H. FUJITA, Seikei University, Musashino, Tokyo, Japan; Aichi Univ. Educ., Kariya, Aichi, Japan; IIS, Univ. Tokyo, Meguro, Tokyo, Japan

The realization of a novel lubric system, making it possible for nano- and micromachines to move easily, have been strongly desired. In this talk, atomic-scale friction, peeling and shear in carbon and silicon nanostructures are discussed.
First the ultralow friction mechanism of graphite/C60 interface is studied using molecular mechanics simulation. Anisotropy of friction of graphite/C60 interface is found, where the maximum and minimum friction appears for the commensurate and other scan direction, respectively. It is clarified that the small rotation and elastic contact of C60 molecules contribute to the ultralow friction.
Next the nanoscale shear and friction acting between the opposing Si tips are studied by molecular dynamics simulation. During the shear process, the characteristic transition of the dynamics of the nanocontact appears as follows: First the shear of the nanocontact at the interface is dominant. During the shear process, nanocontact slides at Si/Si interface. Then the elongation of the nanowire becomes dominant until it breaks. These simulated features are in good agreement with those obtained by MEMS in TEM measurement. This work can contribute to understanding dynamics of the single real contact area.


CC-5:IL02  Insights into Friction of Carbon Based Ceramic Tribomaterials by MD Simulations
M. MOSELER, Fraunhofer Institute for Mechanics of Materials IWM, Freiburg, Germany

Although ceramics are used in many tribological applications (ranging from water pumps to watches), the microscopic mechanisms underlying running-in, friction and wear of ceramic materials are still not well understood. In this talk, experimental investigations of carbon based ceramics will be combined with classical molecular dynamics simulations to provide deep insights into the running-in and wear mechanisms of tungsten-carbide [1,2] and silicon-carbide tribo systems.
[1] P.Stoyanov, P.Romero, T.T. Järvi, L.Pastewka, M.Scherge, P.Stemmer, A.Fischer, M.Dienwiebel, M.Moseler, Experimental and atomistic investigation of the third body formation process in dry tungsten/tungsten-carbide tribo couples. Tribo. Lett. 50, 67(2013)
[2] P.Stoyanov, P.Stemmer, T.T. Järvi, R.Merz, P.Romero, M.Scherge, M.Kopnarski, M.Moseler, A.Fischer, M.Dienwiebel, Friction and wear mechanisms of tungsten-carbon systems: A comparison of dry and lubricated conditions, ACS Appl. Mat. and Interf. 5, 6123 (2013)


CC-5:IL03  Tribochemical Reaction Dynamics by First-Principles and Tight-Binding Quantum Chemical Molecular Dynamics Methods
M. KUBO, Fracture and Reliability Research Institute, Graduate School of Engineering, Tohoku University, Sendai, Japan

Diamond-like carbon (DLC) and its related materials, such as CNx and SiC, have gained much attention as super-low friction materials for automotive engines, aerospace equipments, etc. The detailed understanding of the tribochemical reactions of the DLC and its related materials is strongly required for clarifying their super-low friction mechanism and designing more efficient super-low friction materials. Here, classical molecular dynamics simulation was frequently employed to investigate the friction behaviors. However, the classical molecular dynamics method cannot simulate the chemical reaction dynamics. Therefore, we developed our original first-principles molecular dynamics simulator "Violet" [1] and tight-binding quantum chemical molecular dynamics simulator "Colors" [2] for the elucidation of the tribochemical reaction dynamics [3,4]. In this conference, various applications of our developed simulators to the tribochemical reaction dynamics of DLC and its related materials will be introduced.
[1] T. Shimazaki and M. Kubo, Chem. Phys. Lett., 503 (2011) 316.
[2] M. Koyama, M. Kubo, A. Miyamoto et al., J. Phys. Chem. B, 110 (2006) 17507.
[3] K. Hayashi, M. Kubo et al., J. Phys. Chem. C, 115 (2011) 22981.
[4] K. Hayashi, M. Kubo et al., Faraday Discuss., 156 (2012) 137.


CC-5:IL04  Atomistic Understanding of Wear in Diamond and other Carbon Materials
L. PASTEWKA, Fraunhofer Institute for Mechanics of Materials, Freiburg, Baden-Württemberg, Germany

Diamond and amorphous carbon (aC) are prototypical examples of wear resistant materials. Yet, these materials wear down, but little is known about the atomic scale processes that cause wear. Molecular dynamics is ideally suited to gain a deeper understanding of the underlying wear processes. Such atomic-scale simulations reveal that both, mechanical and oxidative wear actions are active. Mechanical action transforms the material to a weaker state that is then easily oxidized. For diamond, we find a transition to an aC, while we find a high-density-low-density aC-aC transition for amorphous thin films. The velocity of the diamond/aC interface depends crucially on the diamond surface orientation with the highest speed found for (110) surfaces that are rubbed in the (001) direction, while the lowest interface speed was observed for the diamond (111) surface. High-density aC itself transforms even faster to a low density state that then succumbs to wear. These findings are in perfect agreement with a 600 years old experimental knowledge of diamond polishers, and with recent experiments comparing wear in diamond and amorphous carbon thin films.

 
Session CC-6 - Testing and Characterization

CC-6:IL01  In-Situ Observation of Topography Evolution Wear Debris Generation of Metal Surfaces
M. DIENWIEBEL, P. STOYANOV, T. FESER, MicroTribology Centre µTC, Karlsruhe Institute of Technolog and Fraunhofer IWM, Plinztal, Germany

During sliding of metallic surfaces in dry or lubricated conditions the near surfaces undergo significant changes in terms of topography, composition and microstructure [1] and a so-called “third body” [2] develops. The third-body formation strongly influences the frictional and wear behavior of the system.
In this talk we present several experiments on pure metals and alloys that were performed using a novel experimental platform for the on-line correlation of friction, wear and topography under lubricated sliding [3]. Fast topography data is measured in real time by digital holography microscopy (DHM), wear is measured by the Radionuclide wear technique (RNT) and the nanoscale topography is obtained in-situ by liquid atomic force microscopy (AFM). The tribological systems that we recently studied include α-brass (CuZn) sliding against steel [4], tungsten and tungsten carbide [5, 6].
References
[1] M. Scherge, D. Shakhvorostov, K. Pöhlmann, Wear, 255 (2003) 395-400.
[2] M. Godet, Wear, 100 (1984) 437-452.
[3] S. Korres, M. Dienwiebel, Rev. Sci. Instr., 81 (2010) 063904.
[4] T. Feser, P. Stoyanov., M. Dienwiebel, Wear, 303 (2012) 465-472
[5] P. Stoyanov et al. , Tribol. Lett., 50 (2013) 67-80.
[6] P. Stoyanov et al., ACS Appl. Mat. & Int.s, 5 (2013) 6123-6135.


CC-6:IL02  Surface Chemical Characterization of Tribological Films Formed under Boundary Lubrication Conditions
A. ROSSI, Dipartimento di Scienze Chimiche e Geologiche, Università degli Studi di Cagliari, Monserrato (Cagliari), Italy

Progress in analytical spectroscopic methods and in the instrumentation for tribological measurements have contributed in the last decades to the understanding of the mechanism of growth and stability of tribological films. Tribological films (also called tribofilms) are layers that are formed on two counterparts that move in relative motion to each other. These films play an important role in reducing friction and/or wear and their presence may contribute to saving energy and reducing the amount of CO2 produced in an engine. Tribofilms are usually formed in presence of compounds that are added to lubricant oils. The most commonly used additives contain metals such as zinc and non-metallic elements such as as sulfur and phosphorus. The need for reducing the amount of these elements in the environment—in agreement with European regulations—has stimulated research in tribology by means of surface analytical methods that offer the unique opportunity to characterize surfaces that are in mechanical contact.
In this talk the results obtained in the characterization of tribofilms by means of X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and in situ attenuated total reflection infrared spectroscopy (ATR FTIR) will be reviewed.
X-ray photoelectron spectroscopy has become a very important source of information on surfaces, thin layers and interfaces in the investigation of non-ideal samples such as tribofilms. Nowadays it is possible to use very well focused beams for exciting the sample down to less than 10 μm, so that detailed chemical-state information, composition and thickness of the tribological films and composition of the interface within the reaction layer and the substrate can be obtained uniquely from the contact areas of the two counterparts. Furthermore, imaging capabilities, as well as angleresolved XPS allow the 3D-representation of chemical species.
Complementary to XPS is ToF-SIMS. Recent bismuth-cluster sources have become the standard analytical tools for obtaining high-resolution mass spectra, also in the high mass range, and for obtaining images with a lateral resolution down to 80-100 nanometers. It provides not only elemental but also molecular information.
The results obtained with a recently developed in situ ATR FT-IR tribometer that allows the identification of the functional groups during the sliding of the two counterfaces will be also presented and the strengths of ex situ analytical methods will be discussed.


CC-6:IL03  Tribology in Full View, from Atomic Wear to Hip Replacements
L.D. MARKS, Department of Materials Science and Engineering, Northwestern University, Evanston, IL, USA

Friction is a pervasive problem, by some estimates consuming about 5% of the GDP of the economies of the developed world, and a recent analysis has indicated that about one third of the fuel energy in automobiles goes to overcoming frictional losses. While the importance of minimizing friction can be traced back at least as far as the tomb of Tehuti-Hetep, circa 1880 B.C, where a man can be seen pouring a lubricant to assist moving a statue, there are still many unknowns in the field of tribology which encompasses friction as well as other critical processes such as wear and lubrication. For many of the phenomena in tribology there are still numerous unknowns, due in large part to what has been called the buried interface problem. The triboactive layer, is almost always hidden by the materials on both sides of it so the exact details of what is occurring are often hidden, only accessible by post-facto analyses and sometimes a matter for debate. While there have been several attempts to image the triboactive layer directly at the atomic scale dating from the original work by Gane and Bowden,  progress has been slow. Over the last few years we have been developing both models from a materials science viewpoint via dislocations as well as in-situ techniques for imaging the buried interface. Related to this (perhaps not obviously) we have recently become involved in understanding the nanoscale tribology of hip replacements, including the perhaps surprising observation of a graphitic layer in-vivo that appears to play a major role in reducing implant failures.
This talk will focus upon some of the recent results, ranging from more basic observation such as connecting wear fragment size and a new layer-by-layer wear mechanism to the standoff distance of interfacial dislocations through the formation of graphitic materials in-vivo as well as some direct observations of wear and sliding at the atomic scale.


CC-6:IL04  In-Situ TEM Observation of Nanofriction at a Single Asperity
H. FUJITA, Institute of Industrial Science, The University of Tokyo, Tokyo, Japan

The real-time observation of deformation at a nanoscale junction provides us novel experimantal results toward understanding the mechanisms of friction and lubrication. Our micromachine placed and operated in a TEM allowed us to measure the deformation, force and cross-sectional area of a single asperity during shear testing.
We prepared tips of bare Si and those coated with Ag, and DLC (diamond like carbon) films and brought them into contact. For Si and Ag cases, a nano junction was formed at the contact. Then we applied shear force to the junction, whose size was typically 2-5 nm thick and 3-10 nm long. Typically, the tip displacements of 2-10 nm were observed during the shear testing. Each material showed very different behaviors; Si contact elongated much longer than Ag. The shear force was 10-100 nN. Elongation motion was smooth for Si but step-wise for Ag like a stick-slip motion. The size of steps (0.3 nm and 0.6 nm) corresponds well to the theoretical sliding distance of 0.29 nm calculated from the lattice spacing along the sliding plane. For the DLC interface, no contact but nano balls appeared between two tips. The ball rotated when shear load was applied to the interface.


CC-6:L05  Frictional Property and Crystal Structure of ZnO Coatings Analyzed by a Combinatorial Technique
M. GOTO¹, M. SASAKI², A. KASAHARA², M. TOSA², ¹International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Ibaraki, Japan, ²High Temperature Materials Unit, National Institute for Materials Science, Tsukuba, Ibaraki, Japan

An advanced technique for investigating the frictional property of materials, combinatorial tribology, is newly proposed. The crystal preferred orientation of ZnO coating films on stainless-steel substrates was markedly changed with the magnitude of an applied load, which was observed by X-ray diffraction analysis with micropoint focus X-ray optics. Also the dependence of the friction coefficient on the crystal preferred orientation was measured. Using the new method, it is possible to find the appropriate crystal preferred orientation for coatings with the desired value of the friction coefficient. Therefore, combinatorial tribology is expected to be an effective method for tribology research.

 
Session CC-7 - Tribology Applications

CC-7:IL01  Development of Multi-component Single Alloying Targets for the Easy Preparation of the Low Friction Nanocomposite Coating Applicable to Automobile Engine Parts
KYOUNG IL MOON¹, J.H. SUN², C.H. LEE², S.Y. SHIN², ¹Plasma Enhanced Technology Development Team, Korea Institute of Industrial Technology,  Incheon, Republic of Korea; ²Advanced Fusion Process R&D Group, Korea Institute of Industrial Technology, Incheon, Republic of Korea

Significant researches have been devoted to the preparation of nano-composite films to synthesize hard and super-hard thin films composed of ceramic/ceramic and ceramic/MeN nano composite. However, both hardness and elastic modulus tend to be high, and high elastic modulus of the films can cause intrinsic mismatch between substrate and thin films. It is also known that a high ratio of hardness to elastic modulus (H/E) is indicative of good wear resistance in a disparate range of materials. Therefore, new nc-MeN/metal matrix films with high H/E index which can enhance durability and get low friction properties have been suggested. This study reports on the structure and properties of nc-Zr(Al)N/Cu films synthesized by DC magnetron sputtering process with amorphous single target composed of Zr-Al-M-Cu bulk metallic glass alloys. Also, Zr-Al-M-Cu amorphous thin films are deposited by DC magnetron sputtering process with the same alloyed target. The nanocomposite coating had a very low friction coefficient in lubricant condition even compared with the commercialized DLC coating that was already used in automobile parts. So it could replace the DLC coating in some engine parts.


CC-7:IL02  Tribology of Machine Elements in Hydrogen Energy Systems
J. SUGIMURA, Kyushu University, Fukuoka, Japan

This paper overviews the studies on friction and wear of materials for machine elements used in hydrogen energy systems. These include alloys and coatings for valves, polymeric materials for dynamic seals and piston rings, and steels for bearings. Dry sliding of metals and alloys in hydrogen depends more or less on trace oxygen and water through surface oxidation. Diamond like coatings exhibit excellent friction and wear behaviors in hydrogen, while and there are slight effect of trace impurities, and also delamination may occur by hydrogen uptake. In rolling-sliding contact of steels, acceleration of hydrogen-assisted flaking failure depends on contact conditions and lubricants, while oxide films formed on steel surfaces show resistance against hydrogen permeation. Tribo-chemical reactions at metal surfaces also affect friction and wear of polymers used in dynamic seals in valve and piston rings for compressors. These effects are enhanced in hydrogen at ultra-high pressure.


CC-7:IL03  Novel Super-elastic Materials for Advanced Bearing Applications
C. DELLACORTE, NASA, Glenn Research Center, Cleveland, OH, USA

Tribological surfaces of mechanical components encounter harsh conditions in terrestrial, marine and aerospace environments. Brinell denting, abrasive wear and fatigue often lead to life-limiting bearing and gear failures. Novel superelastic materials based upon Ni-Ti alloys are an emerging solution. Ni-Ti alloys are intermetallic materials that possess characteristics of both metals and ceramics. Ni-Ti alloys have intrinsically good aqueous corrosion resistance (they cannot rust), high hardness, relatively low elastic modulus, are chemically inert and readily lubricated. Ni-Ti alloys also belong to the family of superelastics and, despite high hardness, are able to withstand large strains without suffering permanent plastic deformation. In this paper, the use of hard, resilient Ni-Ti alloys for corrosion-proof, shockproof bearing and gear applications are presented. Through a series of bearing and gear development projects, it is demonstrated that Ni-Ti's unique blend of materials properties lead to significantly improved load capacity, reduced weight and intrinsic corrosion resistance not found in any other bearing materials. Ni-Ti thus represents a new materials solution to demanding tribological applications.


CC-7:IL04  Carbon Based Coatings for Hermetic Compressor Applications
J.D. BIASOLI DE MELLO, Universidade Federal de Uberlandia, Universidade Federal de Santa Catarina, Florianopolis, Santa Catarina, Brazil

Household refrigeration represents 17.3% of home energy consumption in the USA and 47% in Brazil. This article overviews a multidisciplinary approach to develop a traditional hermetic compressor (oil lubricated, with several rotating parts), into an oil-less, linear motion, innovative compressor, with improved efficiency, versatility and sustainability. This involves the development of surface engineering processes combining purpose-oriented phases applied to soft substrates to achieve high wear resistance and load support and low friction coefficient. Initially, the role of the environment (air, CO2 and R600a) on the tribological behaviour of a commercially available Si-rich multifunctional DLC coating deposited on AISI 1020 steel is illustrated. In sequence, the influence of the thickness of different layers (DLC and CrN) on sliding wear is analysed. Results are presented using an original approach (3D triboscopic maps) for two distinct configurations (increasing load and constant load) and findings are confronted with numerical simulations using Film Doctor®. Finally, a low cost process to obtain a multifunctional coating (different nitrided layers + DLC) is described, which uses a unique thermal cycle reactor capable of coating parts in industrial scale with reduced cost.


CC-7:IL05  Tribology of Functional Coatings for High Temperature Applications
B. PRAKASH, C. COURBON, J. HARDELL, Luleå University of Technology, Luleå, Sweden

The last decades have seen rapid development of coatings and their usage in diverse applications, from human body implants to space mechanisms. Their potential is also being explored for tribological contacts subjected to high temperatures, e.g., aerospace, power generation, metal working etc. From a tribological viewpoint, operation of a system above ~ 300 °C means that conventional lubricants will decompose/degrade. The usage of coatings is a way of controlling friction and wear in systems operating at high temperatures. Several coatings including TiAlN, CrN and carbon based coatings are being proposed. However, in most cases these have been studied at room temperature and their high temperature tribological performance has not been adequately investigated. The high temperature tribology research at the authors' laboratory is mainly directed towards the tribological aspects of hot stamping of high strength steels. High temperature studies (up to ~ 1000 °C) involve not only coatings on tool steel but also on the high strength steel surfaces. Frictional behaviour, wear, and material transfer (galling) at elevated temperatures have been the subject of investigations. This talk will present the salient results obtained so far and will also highlight the need for future research.
 
 
Poster Presentations

CC:P01  Effect of Different Form of Carbon Addition on the Wear Behaviour of Copper Based Composites
C. CHMIELEWSKI, A. PIATKOWSKA, K. PIETRZAK, A. STROJNY-NEDZA, Institute of Electronic Materials Technology, Warsaw, Poland

Copper-carbon composite materials are very promising functional materials used as electrical contact devices due to their high electrical conductivity, thermal conductivity and excellent wear resistance. In present study the influence of carbon forms (carbon nanotubes, graphite nanopowder, graphene) on the properties of copper matrix composites was examined. The composites were fabricated via power metallurgy method. The optimal parameters of hot-pressing process in vacuum were fixed as follow: temperature 600 °C, pressure 415 MPa, time 30 min. The friction process of the composites was provided in a ball-on-surface apparatus under dry conditions. The friction and wear behaviour of copper with 5 vol.% of carbon were investigated. Scanning electron microscopy (SEM) was used to analyse the worn surfaces and debris, and finally wear mechanism was discussed.